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1978 evinrude 70 hp 3 cyl hard starts and wont idle without a bit of choke

J

johnyrude87

New member
I have a new to me 1978 evinrude 70 hp that runs realy great at wot on a 17 ft specktrum boat I get 32 mph at wot... rebuildt the carbs cleaned them realy well and installed new kits my problem is it his hard to start and wont idle slow enough for fishing will idle all day just rpms are to high I have the factory service manual and have worked on plenty of outbaords in the past I have done the linc and synk not once but 3 times to make sure all linkages a are where hey should be and that well in gear that the roller is not touching the cam at idle but lined up with the bottom mark on the cam just about to touch but not touching and that the throttle plates in the carbs are 100 percent closed at idle the problem seems to me to the motor is getting to much air from somewhere if I put the choke on just barley on she idles/trolls perfect rpms drop to where the should be and will idle all day but with the choke off she is idleing realy high probley around 1000 rpms in the lake and warmed up i don't have a rpm gage just going by ear she also during cold starts wont run with the choke on if I choke and try to start she fires once and then dies then i turn choke off raise warm up leaver she fires right up the idle stop screw is backed way off so I know that's not the problem I am thinking its getting extra air from somewhere maybe bad read valves or a leaking intake manifold gasket any help how to check the reads or gasket would be amazing so thanks for any input oh and also the control cables are new no slack in them went full throttle and back a whack of times to make sure the linc in sync is correct has great compression and spark fresh fuel mixed 50:1 this thing is driving me crazy
 
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Are you able to adjust idle timing on that model? Couldn't tell by the parts diagram. Might be advanced a little too much. Did you clean the idle air jets by taking them out of the carb body and soaking them in carb cleaner? Also, try spraying some wd40 or similar around the carb bases, manifold gaskets, etc. and look for a change in rpm to find an air leak.
 
yes carbs have been completely gone threw both the high speed and low speed orfices are clean there is the idle stop screw and if u turn one way would increase the idle turn out it would decreas the idle I have that screw backed pretty much all the way out so I don't think its anyting to do with that I will spray with some wd40 and check the gasket but how about checking the read valves behind the carb at this point I am 100 percent certain its nothing to do with the carbs or in any of the ajustments done the linc and synk and few times now and everything is bang on should be purring like a kitten but will only way to drop the rpms to idle properly is with the choke on just a bit
 
When you cold start the motor the high idle lever needs to be used while choking the motor. You need to get a tach on that motor because idle speed is set in gear and warm. Have you adjusted the throttle cable to pull the linkage against the idle screw. Hopefully the throttle cable will do the trick. if it does the trick you shoud get a gap between the throttle cam and roller. LEAVE timing alone unless somebody moved it or something catastrophic happend the timing is fine.
 
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im not realy conserned with the hard starts I will try lifting the warm up lever well choking next time I am down at my trailer most likely the long weekend but I put the new throttle cable on already dident make any difference like I said have checked all the messurements also known as linc and sync I also even well in gear in the water moved the throttle control arm back slowly by hand I don't think its a timing advance issue at all cuz when I do that the slightest bit moving the throttle control arm by hand instead of the cable all I get is a lean sneaze and it dies only way to lower the idle rpm so it runs good is to choke it well ingear or in neutral in the lake so I am starting to think for sure its leaking air somewhere and not at the carbs because I replaced all fuel lines when I did the rebuild of the carbs and new carb gaskets and air box gakets
 
anyone know the best way to check the reads on these motor do I just pull the carbs and make sure they are closed or do I leave the carbs on a check to see if gas is spaying out the front of them thanks for the help so far and any feature help guys
 
I would re -do the link and sync and make sure you have about a 1\4-1\8" gap between the roller and cam. You want the butterflies on the carbs to open when the middle of the roller hits the mark.
 
I am 99 percent sure that's they way it is when the roller makes contact it is dead center of the bottom mark on the cam and the throttle plates are for sure closed will double check again to make sure tho
 
if all thos messurements are right and its not a leaking gasket or read valves is there anything else that could cause it only to idle at lower rpms with the choke on I am pretty sure the igniton system is fine on this motor fuel pump seems to be pumping good too I haven't tried to move the throttle arm well pumping the ball on the tank I guess that is something else I could try I just wanna get this thing trolling slower so I can get out fishing on the long weekend thanks for your help so far guys I do have a spair complete igniton system so anything else that could cause it I could also check
 
Going to jump in here with a possibility? Your not going to like it, but bear with me. First I guess you don't know what your WOT RPMs are? I don't think you said you had a tach. These motors like to turn a full 6000 at full throttle. With a large prop which might keep it from full potential it would load the motor for a poor idle. Just a thought?
The next one is really unpopular. If your motor's idle just fades away, dies & always has to be choked to restart then you have to question your cylinder to piston wall fit on looper engines. Particularly 2 & 3 cylinder OMC engines. They have very large ports & wear will cause the fuel charge escape on the down stroke.

Dan in TN
 
By choking you are wet sealing the cylinders with fuel & oil. You can check this condition with a timing light. Late evening you can hook up a timing light on each cylinder & shine it across the corresponding cylinder. You can see the fuel charge puffing out the front of the carb. The timing light freezes it in action.
Sometimes a slightly larger idle jet will get you by for a while. Your engine has a .032. Maybe a .034 or .035 would help you out. I should have some if this proves out to be your problem. At least it will tell you if your on the right track.
Let us know what you find out.

Dan in TN
 
49 cid 70 hp motors like yours run to 5500 rpm max rpm. If all the posts would have been read the op is not even using the high idle lever. More of a learning how to start it problem. The later 86 and newer 56 cid 3 cyl blocks to 6000 rpm.
 
Two thoughts: Can you borrow a timing light and see if you are in spec at idle? Can you just run it at idle with the choke on and leave it that way while you're trolling? If so, just go fishing and forget about it.
 
A timing light will usually show correct timing , even with a sheared flywheel key.----If you have to use choke to keep it running there is an issue with carburetors.----Best to trouble shoot and fix.
 
Good to know, just figured that since timing can affect idle speed and is the way that idle speed is set on many motors, that it was worth checking. Otherwise it sure sounds like a lean condition. To the OP, was the idle problem there before or after you rebuilt the carbs? Are the idle jets the right ones? Looks like they should be #32.
 
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